The present invention relates to a method of reproducing audio signals and an audio player, more precisely relates to a method of reproducing audio signals which have been recorded on a recording medium, e.g., a compact disk (CD), as voice, and an audio player employing said method.
In some cases, the audio reproducing speed of an audio player, such as a CD player, a tape recorder, or a video player, must be slower or faster than the normal reproducing speed. For example, the reproducing speed is accelerated when a listener wants to listen the recorded audio data in a short time. On the other hand, the the reproducing speed is made slower if the audio data was rapidly recorded.
Conventionally, the rotational speed of a CD or running speed of a tape is changed to change the reproducing speed of the audio player.
By the conventional method of changing the reproducing speed, frequency of the audio signals, which have been read from the recording medium, e.g., the CD, is also changed according to the change of the reproducing speed, so that the tone of the reproduced voice is changed and worsened.
A conventional method of changing the reproducing speed while keeping the original tone will be explained with reference to FIG. 8. Original audio signals (a) are divided into a plurality of frames (A1, A2, A3, A4, A5, A6 . . . ), each of which has fixed time length (t). The audio reproducing speed can be changed by selecting the frames (A1, A2, A3, A4, A5, A6 . . . ). To reproduce audio signals twice as fast as the normal reproducing speed, for example, the frames (A1, A2, A3, A4, A5, A6 . . . ) are partially thinned out, and the audio signals corresponding to the frames left, e.g., the frames (A1, A3, A5 . . . ), are reproduced as voice. By this method, reproducing time of reproduced audio signals (c) can be half of original recording time. Namely, the listening time can be reduced to half. Further, frequency of the original audio signals (a) or cycle time (T) thereof is not so changed. Consquently, the audio signals (a) can be reproduced as the voice with original tone.
If the audio signals corresponding to the selected frames (A1, A3, A5 . . . ) are merely connected, the signals are not met in connecting sections (B1, B2, B3, B4) as shown audio signals (b), and uncomfortable noise is produced in each connecting section (B1, B2, B3, B4).
To reduce the noise, the signal level at an end point of one selected frame, e.g., the frame (A1), and signal level at a starting point of an adjacent selected frame, e.g., the frame (A3), are functionally coincided each other. An example of functional formula is, EQU W(n)=0.5-0.5 cos(2.pi.n/M)
n: signal level in the frame; and PA1 M: n=0, 1, . . . M. PA1 filtering original audio signals, which have been recorded on a recording medium, to extract basic audio signals; PA1 detecting zero-cross points in the basic audio signals; PA1 dividing the original audio signals into a plurality of frames on the basis of the zero-cross points on a time axis; and PA1 thinning out the frames; and PA1 reproducing the original audio signals on the basis of the frames left so as to accelerate reproducing speed. PA1 filtering original audio signals, which have been recorded on a recording medium, to extract basic audio signals; PA1 detecting zero-cross points in the basic audio signals; PA1 dividing the original audio signals into a plurality of frames on the basis of the zero-cross points on a time axis; and PA1 reproducing the original audio signals by repeating the frame so as to make reproducing speed slower. PA1 a filtering section filtering original audio signals, which have been recorded on a recording medium, to extract basic audio signals; PA1 a detecting section detecting zero-cross points in the basic audio signals; and PA1 a signal processing section dividing the original audio signals into a plurality of frames on the basis of the zero-cross points on a time axis, thinning out the frames, and reproducing the original audio signals on the basis of the frames left so as to accelerate reproducing speed. PA1 a filtering section filtering original audio signals, which have been recorded on a recording medium, to extract basic audio signals; PA1 a detecting section detecting zero-cross points in the basic audio signals; and PA1 a signal processing section dividing the original audio signals into a plurality of frames on the basis of the zero-cross points on a time axis, and reproducing the original audio signals by repeating the frame so as to make reproducing speed slower.
By this process, the original audio signals (a) can be formed into audio signals (c) which are continuous of the connecting sections (B1, B2, B3, B4), so that the uncomfortable noise in the reproduced audio signals (voice) can be reduced.
However, the conventional method has following disadvantages.
In the conventional method, the signal level of the original audio signals (a) in the connecting sections (B1, B2, B3, B4) must be changed to a prescribed level, e.g., zero, so the cycle time of the changed audio signals (c) in some connecting sections are quite different from that of the original audio signals (a). If the cycle time of the changed audio signals (c) is partially quite different from that of the original audio signals (a), the tone of the reproducing audio signals (voice) is quite different from the original voice. Further, the frequency of the reproduced audio signals (c) corresponding to the connecting sections (B1, B2, B3, B4) is also different from the original audio signals (a), so quality of sound or voice decreases.